Prime Minister Malcolm Turnbull says if North Korea launches an attack on the United States, Australia will join the conflict.

"So be very, very clear on that. If there's an attack on the US, the ANZUS Treaty would be invoked and Australia would come to the aid of the United States, as America would come to our aid if we were attacked." Turnbull told 3AW.

Yesterday, Julie Bishop said there was no "automatic trigger" for Australia to join a war between the US and North Korea, because Australia was not a party to the armistice declared at the end of the Korean War in 1953.

She acknowledged the ANZUS treaty imposed separate obligations on both countries but also said it only required Australia and the US to "consult" with each other, if either country was threatened or attacked.

Anxiety over North Korea's nuclear tests has also stoked debate about whether Australia needs to develop its own missile defence shield.

Former prime ministers Kevin Rudd and Tony Abbott have separately called for the Government to consider developing a shield which could provide protection from intercontinental ballistic missiles.